The present invention relates to an exposure apparatus, a semiconductor device and a photomask, particularly to an exposure apparatus for producing a semiconductor device comprising an integrated circuit having a fine pattern with a line width of 100 nm or less using a fluorine laser as an exposure light source, a semiconductor device obtainable by such an exposure apparatus, and a photomask.
Heretofore, in a photolithographic technology, an exposure apparatus has been widely utilized which transfers a fine circuit pattern on a wafer to produce a semiconductor device comprising an integrated circuit. Along with high integration and high functionality of an integrated circuit, the exposure apparatus is required to form an image of a circuit pattern with high resolution on a wafer with a deep focal depth to have a fine circuit pattern drawn with a narrower line width, and shortening of the wavelength of the exposure light source is being advanced. The exposure light source has been advanced from conventional g-line (wavelength: 436 nm) or i-line (wavelength: 365 nm), and now, a KrF excimer laser (wavelength: 248 nm) or an ArF excimer laser (wavelength: 193 nm) is being used. Further, as a light source of next generation which is required to draw a further finer line with a width of 100 nm or less, a fluorine laser (wavelength: 157 nm) is expected to be a prospective candidate.
In an optical system of an exposure apparatus using a KrF excimer laser or an ArF excimer laser as a light source, a synthetic quartz glass is employed, since it is transparent over a wide wavelength range from a near infrared region to a vacuum ultraviolet region, and it is excellent in various properties such that the thermal expansion coefficient is very small so that it is excellent in dimensional stability, and it has high purity. However, a synthetic quartz glass having a large OH group content, which is used for a KrF excimer laser or an ArF excimer laser, has a low transmittance in a region of wavelengths of not longer than 165 nm, and as such, it is not useful for a fluorine laser which is expected to be a light source of next generation.
Further, with a synthetic quartz glass having the OH group content reduced in order to improve the transmittance in a region of wavelengths of not longer than 165 nm, the transmittance sharply decreases as the wavelength of the transmitted light becomes shorter than about 170 nm.
Accordingly, in a case where a synthetic quartz glass is to be used as an optical member in an exposure apparatus employing a fluorine laser as a light source, it will be an important subject to improve the transmittance.
Further, the optical system of an exposure apparatus is constituted by a combination of many optical members such as lenses and prisms. Accordingly, an improvement in transmittance of each individual optical member will bring about a large improvement in transmittance when integrated as an entire optical system.
However, a process for efficiently and conveniently producing a synthetic quartz glass which has an improved transmittance in a region of wavelengths of not longer than 165 nm which is the wavelength region of fluorine laser and which can be applied to an optical member of an exposure apparatus using a fluorine laser as a light source, has not yet been proposed, and has been a serious objective with a view to developing an exposure apparatus of next generation.
The present invention has an object to provide an exposure apparatus for producing a semiconductor device comprising an integrated circuit having a fine pattern with a line width of 100 nm or less using a fluorine laser beam as an exposure light source, and a semiconductor device obtainable by such an exposure apparatus.
The present invention also has an object to provide a photomask which is useful for forming a fine pattern with a line width of 100 nm or less on a wafer by means of an exposure apparatus using a fluorine laser as a light source.
The present invention provides an exposure apparatus employing a fluorine laser (hereinafter referred to as xe2x80x9cF2 laserxe2x80x9d) as a light source, wherein at least one of optical members constituting an exposure light source system, an illuminating optical system, a photomask and a projection optical system, is made of a synthetic quartz glass for an optical member, and said synthetic quartz glass for an optical member has an absorption coefficient of 0.70 cmxe2x88x921 or less at a wavelength of 157 nm.
Further, the present invention provides an exposure apparatus, wherein at least one of optical members constituting an exposure light source system employing F2 laser as a light source, an illuminating optical system, a photomask and a projection optical system, is made of a synthetic quartz glass for an optical member, and said synthetic quartz glass for an optical member is one obtained by a process comprising a step of irradiating a synthetic quartz glass having an OH content of 50 ppm or lower and a hydrogen molecule content of 1xc3x971017 molecules/cm3 or higher, with vacuum ultraviolet light having a wavelength of 180 nm or shorter, to improve the transmittance in a region of wavelengths of not longer than 165 nm.
The present inventors have found that in an exposure apparatus using F2 laser having a wavelength of 157 nm as a light source, an optical member constituting each of an exposure light source system, an illuminating optical system, a photomask and a projection optical system constituting the exposure apparatus, is required to have a high transmittance of F2 laser, and it is effective that the absorption coefficient at a wavelength of 157 nm is 0.70 cmxe2x88x921 or less. It is particularly preferred that the absorption coefficient at a wavelength of 157 nm is 0.30 cmxe2x88x921 or less.
Further, it has been found effective that the optical member has an infrared absorption peak attributable to SiOH stretching vibration at about 3640 cmxe2x88x921.
The present invention provides, as one of optical members, a photomask employing a synthetic quartz glass for an optical member, which has an absorption coefficient of 0.70 cmxe2x88x921 or less at a wavelength of 157 nm and an infrared absorption peak attributable to SiOH stretching vibration at about 3640 cmxe2x88x921.
Further, the present invention provides a photomask employing a synthetic quartz glass for an optical member obtained by a process comprising a step of irradiating a synthetic quartz glass having an OH content of 50 ppm or lower and a hydrogen molecule content of 1xc3x971017 molecules/cm3 or higher, with vacuum ultraviolet light having a wavelength of 180 nm or shorter, to improve the transmittance in a region of wavelengths of not longer than 165 nm.